Question

A phase lag lead network introduces in the output

(a) Lag at all frequencies

(b) Lag at high frequencies and lead at low frequencies

(c) Lag at low frequencies and lead at high frequencies

(d) None of the mentioned

This question was posed to me in a national level competition.

I'd like to ask this question from Pole Placement by State Feedback topic in chapter State Variable Analysis and Design of Control Systems

Answer 1

Right choice is (c) Lag at low frequencies and lead at high frequencies

To explain I would say: A phase lag lead network is the network that is similar to the differentiator and it is used to increase the speed response and increases the stability of the system and this introduces lag at low frequencies and lead at high frequencies.